Document processing systems optically read information from documents, such information may be stored if not used immediately for processing or subsequently displayed to an operator via a terminal or work station. Numerous processing systems may lift portions of the image of a document in order to retain certain fields of information of the document. Additionally, information on the document may be optically read for further processing of the document. In the course of such processing, the optical reading system may be unable to identify a portion of the information, and human intervention is necessary to perform the reading operation. This human intervention involves the displaying of the image of the document to an operator to assist in the recognition of a character or unidentified portion.
Information from a document may be found in layers, such as for example, on a bank check. The bottom layer can be considered the background or the artistic scene found on the front of a check. The next layer may comprise the printing on the check such as the imprinted address of the bank account holder, the bank identifying characters and the check amount field. An additional layer is the actual writing place on the check by the maker of the check. A further layer comprises any subsequent stamps or imprinting done by banks in the processing of the check. The usefulness of the concept of layers involved in processing an image of a bank check is more apparent when examining the images of the back of the bank check.
During processing of bank checks, various stamps are placed on the back of the check. The bottom layer of the image may be considered to be the background or safety pattern of the check. Each stamp found on the back of the check during processing can also be considered to be a separate layer. If each stamp or layer does not overlap, information from each layer is easy to discern as all of the information is found at a single location with no overlap on the back of the bank check. However, in many instances, the stamps will overlap, and it will be difficult to decipher the individual stamps necessary for processing of the bank check. If these overlapping layers could be viewed separately, the image processing systems could better discern the information found on the check from the image data.
Previous attempts to solve the problem of distinguishing between layers of information on a bank check have used a correlator or similar process to make a binary decision. This approach determines whether each picture element (pixel) contains useful information. Some difficulties experienced with this method include distinguishing between overlapping layers and working at an acceptable level on both low and high print contrast ratio images. An additional approach to this problem has been gray scale processing which assigns a different gray shade to each layer of information found on the document. However, gray scale processing presents a problem to an operator in distinguishing one shade from another. This problem becomes more severe when there are more than four shades of gray in the image since the human eye has difficulty in distinguishing between shades of gray.
A need has thus arisen for an image processing system for processing images of documents having multiple layers of information contained on the document. Such a system must assist a human operator in distinguishing between the layers of information so that the image can be readily viewed and recognized.